Local area networks use a network cable or other network media to link nodes (e.g., workstations, routers and switches) to the network. Each local area network architecture uses a media access control (MAC) enabling network interface device (NID) at each network node to share access to the media.
Traditional Ethernet networks (10BASE-T) operate at 10 Mb/s Ethernet protocol, as described by IEEE Standard 802.3; the majority of Ethernet interfaces currently operate at this data rate. However, a newer Ethernet standard, under IEEE standard 802.3 u, accomplishes the faster operation of 100 BASE-T systems, at a 100 Mb/s data rate (i.e., a 125 Mb/s encoded bit rate) using unshielded twisted pair (UTP) physical media. The 100 BASE-T standard defines operation over two pairs of category 5 UTP (100 BASE-TX) and over four pairs of category 3 UTP. The 100 BASE-FX network medium, covered by the 100 BASE-T standard, allows operation over dual fiber optic cabling.
Physical (PHY) layer devices are used to enable the MAC to send and receive digital packet data across an interface that is generic to the different media standards. In particular, PHY devices are configured for translating digital packet data received from a MAC across a standardized interface, e.g., a Media Independent Interface (MII), into an analog signal for transmission on the network medium, and reception of analog signals transmitted from a remote node via the network medium. Hence, the MII connects the MAC to a physical layer (PHY) transceiver configured for a particular network medium, e.g., 10 BASE-T, 100 BASE-FX, or 100 BASE-TX.
Newer PHY devices are designed to operate at different network speeds, depending on the type of network medium and the capabilities of a link partner at the other end of the network medium. In such a case, each PHY device needs to be configured to a setting that is compatible with the configuration settings of the link partner's PHY device.
Auto-negotiation is performed between PHY devices of link partners. For example, autonegotiation is performed as a link startup procedure between a network switch port (or repeater port) and a workstation linked to the switch port via the network medium each time a link to the switch port is connected, powered on or reset. During auto-negotiation, the two PHY devices of the link partners exchange information about their capabilities, and then the PHYs configure themselves to the best operating mode that is common to them.
Hence, the PHY transceivers of the link partners will typically perform auto-negotiation amongst each other to determine the best common operating mode for transmission and reception of data packets. Additional details regarding auto-negotiation are disclosed in Breyer et al., “Switched and Fast Ethernet: How It Works and How to Use It”, Ziff-Davis Press, Emeryville, Calif. (1995), pp. 60-70, and Johnson, “Fast Ethernet: Dawn of a New Network”, Prentice-Hall, Inc. (1996), pp. 158-175.
As described above, the PHY transceivers of the link partners perform auto-negotiation amongst each other to determine the best common operating mode. Each PHY transceiver then supplies any necessary capabilities information to the corresponding MAC via a management data input/output (MDIO) serial interface on the MII.
Newer PHY transceivers, such as the commercially-available Am79C875, “NetPHYT™-4 LP Low Power Quad 10/100-TX/FX Ethernet Transceiver” from Advanced Micro Devices, Inc., Sunnyvale, Calif., integrate a plurality of PHY transceivers onto a single semiconductor chip. However, if a PHY transceiver is configured via autonegotiation, only the NID that was involved in the autonegotiation knows of the results and the other NIDs on the chip have no direct method of determining the results of the autonegotiation.